Wireless energy transfer systems are known to incorporate a first resonator structure (source resonator) that includes a coil configured for transferring magnetic energy and a spaced apart second resonator structure (capture resonator) that also includes a coil configured for receiving the wirelessly transmitted magnetic energy. Such a wireless energy transfer system may be used for electrically charging an energy storage device, such as battery of an electric or hybrid vehicle. In such a system, the source resonator may be located on, or embedded into, a surface for example the floor of a garage or the surface of a parking lot, and the capture resonator may be disposed on a vehicle.
During operation of such a wireless energy transfer system, the vehicle to be charged is parked so that the capture resonator is generally aligned above the source resonator. The source resonator and capture resonator are separated by a distance that approximates a ground clearance of the vehicle which is a typical clearance between the bottom portion of the vehicle's chassis and a ground surface. In some vehicle applications, the ground clearance may be in a range from about 10 centimeters (cm) to 20 cm. In such an arrangement, the ground clearance space between the source resonator and capture resonator is typically large enough to provide room for foreign objects such as aluminum soda cans or steel tools to reside on or near the source resonator. Metallic foreign objects such as these in the vicinity of the source resonator may reduce the energy transfer efficiency of the resonators and may cause undesirable localized heating due to inductive heating of the foreign object. The space between the source resonator and capture resonator may also be large enough to allow small animals, for instance dogs or cats, to come between the resonators. Having an animal between, or in close proximity to, the resonators when the wireless energy transfer system is operating may be a cause for concern. It may be desirable to monitor the source resonator and an area around the source resonator for foreign objects and to control the wireless energy transfer system to prevent or modify system operation when a foreign object is detected.
Wireless energy transfer systems capable of detecting foreign objects have been proposed, see United States Patent Application Number 2011/074346 filed Mar. 31, 2011 by Hall et al. These wireless energy transfer systems typically rely on detecting the heating of a foreign object caused by operation of the system.
The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also be inventions.